The beta-hemolytic streptococcus species are important pathogens responsible for numerous human diseases ranging from superficial infections to more severe illnesses. They include species from serological groups A, B, C and G. Group A Streptococcus bacteria (Streptococcus pyogenes) are accountable for most cases of illness and can result in non-invasive disease such as pharyngitis, scarlet fever, impetigo, cellulitis or erysipelas. Some Streptococcus strains can lead to more severe invasive infections such as toxic shock syndrome, necrotizing fasciitis and septicemia. Additionally, complications of surface infections can result in immune-mediated sequelae. Lancefield's Group B streptococcus (Streptococcus agalactiae) is the predominant cause of neonatal sepsis in neonates and can cause pneumonia in elderly patients. Streptococcal groups C and G were initially recognized as animal pathogens but in recent years have been shown to have a strong potential for human disease. Illness caused by Streptococcal groups C and G generally presents itself similarly as in Group A streptococcus but has not been shown to lead to immune-mediated sequelae. Group C and G streptococci are often present in patients with underlying health problems, are of importance for elderly patients and are dispersed among several streptococcal species.